Fluorine compound - containing composite material and method of preparing same

ABSTRACT

A fluorine compound-containing composite material consists essentially of a metal or polymer matrix and particles or fibers of a polytetrafluoroethylene oligomer having a number average molecular weight of 10,000 or less, the proportion of the number of fluorine atoms to the number of the total atoms at the surface portion of the composite material being 40% or more.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/850,427 filed on Mar. 12, 1992 now abandoned, the entire contents ofwhich are hereby incorporated by reference.

The present invention relates to a fluorine compound-containingcomposite material having a remarkably outstanding water and oilrepellency and lubricity, and a method of preparing the same.

BACKGROUND OF THE INVENTION

Fluorine compound-containing composite materials are conventionallymanufactured by dispersing particles or fibers of a fluorine compoundinto a metal or polymer matrix. For a fluorine compound-metal compositematerial, it is known that by using a composite plating bath prepared bydispersing particles or fibers of a fluorine compound such as fluororesin (e.g., polytetrafluoroethylene resin) and fluorinated graphite(CF)_(n) into a metal plating solution such as nickel plating solutionand codepositing a metal film with the particles or fibers from thecomposite plating bath, a composite plating film having particles orfibers of fluoro resin or fluorinated graphite in a metal matrix can beobtained and the resulting composite plating film has an excellent waterrepellency and lubricity.

A fluorine compound-polymer composite material is prepared by dispersingthe fluoro resin or fluorinated graphite into a polymer such as epoxyresin. Such a fluorine compound-polymer composite material also has anexcellent water repellency and lubricity.

However, the contact angle of the composite material having theconventional polytetrafluoroethylene resin particles dispersed thereinis about 105° and the contact angle of the composite material havingfluorinated graphite particles dispersed therein is 120°. There is ademand for composite materials having a higher contact angle and hence amore excellent water and oil repellency and lubricity.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a fluorinecompound-containing composite material having a remarkably outstandingwater and oil repellency and lubricity.

Another object of the present invention is to provide a method ofpreparing such a fluorine compound-containing composite material.

The present inventors have found that by using a composite plating bathprepared by dispersing polytetrafluoroethylene oligomer particles havinga number average molecular weight of 10,000 or less in a metal platingsolution, a composite film consisting essentially of a metal matrix andthe polytetrafluoroethylene oligomer particles having a number averagemolecular weight of 10,000 or less dispersed therein can be obtainedand, surprisingly, the thus obtained composite film has a contact angleof 150° or more and hence a remarkably outstanding water and oilrepellency and lubricity. We have further found that by contactingfluorine gas to the surface of the composite film obtained, the contactangle thereof is further increased.

As described above, the conventional composite material havingpolytetrafluoroethylene resin particles dispersed therein has a contactangle of about 105°. The dispersed amount of polytetrafluoroethyleneresin particles in the composite material is usually in a range of 20 to40% by volume. If the dispersed amount of polytetrafluoroethylene resinparticles is increased, the contact angle may be increased to someextent. However, even if the dispersed amount can be increased nearly to100% by volume, the contact angle is no longer increased and the waterrepellency is not improved any more. This is recognized from the factthat polytetrafluoroethylene resin film formed on the entire surface ofan article as so-called "Teflon" coating merely has a contact angle ofabout 110°.

As the result of investigating about various fluorinecompound-containing composite materials, the inventors have found thatthe proportion of the number of fluorine atoms to the number of thetotal atoms at the surface portion of the composite material has animportant relation to the contact angle or repellency at the surface.More specifically, the conventional polytetrafluoroethylene resin has anumber average molecular weight of 100,000 or more and substantiallyconsists of CF₂ groups although the end groups are composed of CF₃groups. Therefore, even if the dispersed amount of suchpolytetrafluoroethylene resin in a composite material is increased, theproportion of the number of fluorine atoms at the surface portion of thecomposite material is not so increased and therefore the contact angleor repellency is not so highly improved. The proportion of the number offluorine atoms at the surface portion is about 15% by volume at mosteven if the surface portion is formed only by thepolytetrafluoroethylene resin having a number average molecular weightof 100,000 or more.

On the other hand, when a composite material is prepared by usingpolytetrafluoroethylene oligomer particles having a number averagemolecular weight of 10,000 or less or fluorinated ones prepared bytreating the polytetrafluoroethylene oligomer particles with fluorinegas, the proportion of the number of fluorine atoms at the surfaceportion of the composite material is extremely increased and the contactangle or repellency thereof is surprisingly increased. We have furtherinvestigated and reached to a new finding that it is important toincrease the proportion of the number of fluorine atoms at the surfaceportion in order to attain an increased contact angle resulting in ahigher repellency and that when the proportion of the number of fluorineatoms at the surface portion of the composite material is increased to40% or more, water repellency is remarkable and, to our surprise, acontact angle of nearly 180° can be attained in fact.

Therefore, according to one aspect of the present invention, there isprovided a fluorine compound-containing composite material having acontact angle of 150° or more at the surface consisting essentially of amatrix and particles or fibers of a polytetrafluoroethylene oligomerhaving a number average molecular weight of 10000 or less dispersedtherein, the proportion of the number of fluorine atoms to the number ofthe total atoms at the surface portion of the composite material being40% or more.

According to another aspect of the present invention, there is provideda method of preparing a fluorine compound-containing composite materialcomprising codepositing a metal film with particles or fibers of afluorine compound to an article to be plated from a composite platingbath having said particles or fibers dispersed therein so that acomposite plating film consisting essentially of a metal matrix and theparticles or fibers dispersed therein is formed on the article and theproportion of the number of fluorine atoms to the number of the totalatoms at the surface portion of the composite plating film is 40% ormore.

There is also provided a method of preparing a fluorinecompound-containing composite material comprising codepositing a metalfilm with polytetrafluoroethylene oligomer particles having a numberaverage molecular weight of 10,000 or less to an article to be platedfrom a composite plating bath having said particles dispersed therein,thereby forming a composite plating film having said particles dispersedin a metal matrix on said article.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between the proportion of thenumber of fluorine atoms at the surface portion of a composite materialand a contact angle;

FIG. 2 is a microscopic photograph showing the contact state of a waterdroplet on a nickel-polytetrafluoroethylene oligomer composite materialaccording to the present invention;

FIG. 3 is a microscopic photograph showing the contact state of a waterdroplet on the conventional polytetrafluoroethylene resin film; and

FIG. 4 is a microscopic photograph showing the contact state of a waterdroplet on the conventional nickel plating film.

DETAILED DESCRIPTION OF THE INVENTION

The fluorine compound-containing composite material according to thepresent invention comprises a matrix composed of metal, polymer or thelike and particles or fibers of a fluorine compound or a modifiedfluorine compound surface treated with fluorine gas dispersed therein.At the surface portion (about 20 to about 40 Å thick) of the compositematerial, the proportion of the number of fluorine atoms to the numberof the total atoms is in a range of 40% or more, preferably 40 to 60%.The composite material has a contact angle of 150° or more, preferably160° or more, more preferably 170° to 180°. If the proportion of thenumber of fluorine atoms is less than 40% at the surface portion, such ahigh contact angle cannot be achieved.

The matrix material is not restricted and various materials can be usedas a matrix. For example, metals including nickel, nickel alloys,copper, copper alloys, zinc, zinc alloys, tin, tin alloys and preciousmetals such as silver and silver alloys and polymers including epoxyresins, acrylic resins, methacrylic resins, polyolefins such aspolyethylenes and natural and synthetic rubbers can be used.

The fluorine compound to be dispersed in the matrix should preferably beone in which the proportion of CF₃ group is high. The preferred fluorinecompound is a polytetrafluoroethylene oligomer having a number averagemolecular weight of 10,000 or less because of a high proportion of CF₃group. The lower limit of the molecular weight of the oligomer is notrestricted because the proportion of CF₃ group increases as themolecular weight becomes lower, although the lower limit may be 1,000 ingeneral. The polytetrafluoroethylene oligomer has a lot of end groupscomposed of CF₃ groups as compared with the conventionalpolytetrafluoroethylene resin having a number average molecular weightof 100,000 or more and, therefore, contains more CF₃ groups.Accordingly, the polytetrafluoroethylene oligomer having so many CF₃groups can give a composite material having a higher proportion of thenumber of fluorine atoms. The polytetrafluoroethylene oligomer shouldpreferably have an average particle size of 0.1 to 150 μm, preferably0.1 to 15 μm, more preferably 0.1 to 4 μm. The use of fine particles ispreferred in order to increase the proportion of the number of fluorineatoms at the surface portion.

The conventional high-molecular-weight polytetrafluoroethylene resinhaving a number average molecular weight of 100,000 or moresubstantially consists of CF₂ group. The conventional fluorinated carbon--(CF)_(n) -- substantially consists of CF group. The proportion of CF₃in the conventional polytetrafluoroethylene resin and fluorinatedgraphite is extremely low. Thus they cannot give composite materialshaving the proportion of the number of fluorine atoms of 40% or more atthe surface portion, as described above. However, the conventionalpolytetrafluoroethylene resin and fluorinated graphite modified bytreating them with fluorine gas to introduce CF₃ groups thereto andincrease the content of CF₃ groups can also preferably be used as afluorine compound to be dispersed in a matrix. Of course, the modifiedpolytetrafluoroethylene oligomer treated with fluorine gas is alsopreferably used.

The dispersed amount of the fluorine compound to a matrix is not limitedso long as the fluorine compound is present so that the compositematerial contains the proportion of the number of fluorine atoms of 40%or more at its surface portion.

The composite material having a metal matrix and particles or fibers ofa fluorine compound dispersed therein according to the present inventioncan be obtained by an electrodeposition or electroless deposition methodin which a composite plating bath prepared by dispersing particles orfibers of a fluorine compound containing many CF₃ groups such aspolytetrafluoroethylene oligomer having a number average molecularweight of 10,000 or less into a metal plating solution is used.

The metal plating solution in which the particles or fibers of thewater-insoluble fluorine compound are dispersed may the ordinary oneused for the conventional composite plating. Examples of the platingsolutions include nickel plating solutions such as Watt's bath andnickel sulfamate bath, nickel alloy plating solutions, copper platingsolutions such as copper sulfate bath, copper alloy plating solutions,tin plating solutions, tin alloy plating solutions, zinc platingsolutions, zinc alloy plating solutions and precious metal platingsolutions such as silver plating solutions and silver alloy platingsolution. The metal plating solution is either an electroplatingsolution or an electroless plating solution and comprises theconventional components according to the prior art formulation.

The particles or fibers of the fluorine compound such as thepolytetrafluoroethylene oligomer having a number average molecularweight of 10,000 or less are dispersed in the metal plating solution inan amount of about 1 to about 300 grams, preferably about 10 to about100 grams, more preferably about 50 to about 80 grams per 1 liter of themetal plating solution.

The composite plating bath prepared by dispersing the particles orfibers of the water-insoluble fluorine compound, typically thepolytetrafluoroethylene oligomer, into the metal plating solution maycontain a surface active agent in order to disperse the particles orfibers more uniformly in the bath and increase the codeposition rate ofthe particles or fibers in the metal plating film. As the surface activeagents, perfluoroalkyl type surface active agents can preferably be usedsingly or in combination of two or more, cationic perfluoroalkylammonium salts being most preferred. The amount of the surface activeagent is about 0.001 to about 10 grams, preferably about 0.1 to about 3grams, more preferably about 0.5 to about 0.8 grams per 1 liter of thebath.

The plating conditions may be substantially the same plating conditionsas in the conventional metal plating. In this case, the bath should besufficiently agitated in order to uniformly disperse the particles orfibers in non-agglomerated state or separately into individual piecesthereby obtaining a metal plating film in which the particles or fibersare codeposited with a larger amount and in a uniformly and individuallydispersed state. From this point of view, agitation by ultrasonic waveis recommended.

The codeposited or dispersed amount of the particles or fibers in theplating film should preferably be in a range of about 2 to about 50% byvolume, more preferably about 10 to about 30% by volume.

The composite plating film is formed on an article to be plated. Thearticle is not restricted so long as it can be plated. In other words,the article should have a electrically conductive surface. For example,the article is made of either metal or non-conductive material such asplastics and ceramics having a metal or other conductive layer formedthereon.

A fluorine compound-containing composite material can also be preparedby effect a composite plating film consisting essentially of a metalmatrix and particles or fibers of a fluorine compound codeposited anddispersed therein to a fluorinating treatment.

The fluorinating treatment is carried out by providing and contactingfluorine gas to the surface of the composite plating film. In case thatthe fluorinating treatment is effected to the composite plating filmhaving the above-said polytetrafluoroethylene oligomer dispersedtherein, the proportion of the number of fluorine atoms in the compositeplating film more increases at the surface portion, resulting in furtherimproved surface characteristics including water repellency.

If the composite plating film is heat treated, the fluorinatingtreatment should preferably be carried out after heat treatment. Morespecifically, when the composite plating film is heat treated in air orin an inert gas atmosphere such as nitrogen, argon and helium,particularly in air, the proportion of the number of fluorine atoms inthe composite plating film may be decreased at the surface portionbecause a part of fluorine atoms present at the surface portion arereplaced by oxygen atoms, causing the decrease of the contact angle. Thefluorinating treatment can replace the oxygen atoms introduced upon heattreatment by fluorine atoms and further increase fluorine atoms at thesurface portion of the composite plating film thereby increasing theproportion of the number of fluorine atoms.

The composite material consisting essentially of a polymer matrix andparticles or fibers of a fluorine compound, typically thepolytetrafluoroethylene oligomer, may be prepared by adding anddispersing the particles or fibers into a monomer and then polymerizingthe monomer dispersing the particles or fibers therein.

The fluorine compound-containing composite material according to thepresent invention has a remarkably outstanding water and oil repellencyand lubricity, and therefore can be available for various uses requiringthese properties.

Examples and Comparative Examples are shown below for illustration butnot for limitation.

[Example]

Using a composite electroplating bath having the following formulation,a test piece having 30 mm long, 30 mm wide and 0.1 mm thick waselectroplated by the following plating condition.

Composition of plating bath and plating condition

    ______________________________________                                        Nickel sulfamate     350 g/l                                                  Nickel chloride      45 g/l                                                   Boric acid           40 g/l                                                   Surface active agent (*1)                                                                          0.5 g/l                                                  Polytetrafluoroethylene                                                                            50-70 g/l                                                oligomer particle (*2)                                                        pH of the plating bath                                                                             3.7                                                      Cathode current density                                                                            5 A/dm.sup.2                                             Anode                Nickel                                                   Temperature          43° C.                                            Agitation            Ultrasonic wave                                          Plating time         10 minutes                                               Film thickness       10 μm                                                 ______________________________________                                         (*1) "Megafak" F150, a product of DaiNippon Ink Chemical Co., Ltd.            (*2) Molecular weight 8,000 to 10,000 (number average)                        Average particle size 4 μm (a product of Central Glass Co., Ltd.)     

To the resulting fluorine compound-containing composite materials(composite plating films), the proportion of the number of fluorineatoms at the surface portion and the contact angle were measured by thefollowing methods.

The results are shown in Table 1. The codeposited amount of thepolytetrafluoroethylene oligomer was also shown in Table 1. Method ofmeasuring the proportion of the number of fluorine atoms at the surfaceportion of the composite material

The measurement of the proportion of the number of fluorine atoms to thenumber of the total atoms at the surface portion was conducted by aphotoelectron spectrophotometry using an X-ray photoelectronspectrophotometer ESCA-750 manufactured by Shimazu Seisakusho, Ltd. andirradiating Mg-K.sub.α (125306 eV) as an X-ray source. The correction ofbond energy was made based on gold 4f3/2 spectrum (83.6 eV) as thereference standard. For the quantitative analysis, the spectra of therespective atoms were measured.

In case of the composite materials comprising a polymer matrix describedlater in which hydrogen atoms are contained, the hydrogen atoms cannotbe measured by ESCA 750. So the H/O in the monomer was calculated andthen the number of hydrogen atoms was calculated from the spectralintensity of oxygen atoms.

Method of measuring contact angle

Contact angle was measured at room temperature (25° C.) using a contactangle measurement apparatus G-I manufactured by Etsuma Co., Ltd. Themeasurement was carried out by dropping a droplet of distilled water thediameter of which was adjusted to 1 mm through a microhead from amicrosyringe to the surface of a composite material sample and thenquickly reading the equilibrated contact angle. The contact angle valueshows the mean value of 10 samples.

                  TABLE 1                                                         ______________________________________                                              Proportion of the        Codeposited                                          number of fluorine       amount of                                      Sample                                                                              atoms at the surface                                                                          Contact  the oligomer                                   No.   portion (%)     angle    (% by volume)                                  ______________________________________                                        1     56              173°                                                                            30                                             2     40              160°                                                                            25                                             3     52              170°                                                                            28                                              4*   48              165°                                                                            30                                              5**  58              179°                                                                            30                                             ______________________________________                                         *Sample obtained by heat treating Sample No. 1 at 320° C. for 5        hours in air.                                                                 **Sample obtained by contacting fluorine gas to the surface of Sample 4       for 2 hours at a fluorine pressure of 760 mmHg.                          

[Comparative Example]

The above composite plating process of Example was repeated exceptpolytetrafluoroethylene resin particles having a number averagemolecular weight of more than 100,000 were used instead of thepolytetrafluoroethylene oligomer particles. In the resulting compositeplating film, the proportion of the number of fluorine atoms at thesurface portion of the film was 16%, the codeposited amount of thepolytetrafluoroethylene resin particles in the film was 30% by volumeand the contact angle was 105°.

Further, for comparison purposes, the proportions of the number offluorine atoms at the surface portion as well as contact angle wereevaluated for a nickel-fluorinated graphite composite material obtainedby the same procedure as in Example except that fluorinated graphiteparticles were used instead of the oligomer particles, a compositematerial consisting of polymethylmethacrylate resin matrix andfluorinated graphite particles dispersed therein, and compositematerials consisting of epoxy resin matrix and fluorinated graphiteparticles or polytetrafluoroethylene resin particles having a numberaverage molecular weight of more than 100,000 dispersed therein.

The results are shown in FIG. 1.

As is evident from the results of FIG. 1 which shows the relationbetween the proportion of the number of fluorine atoms at the surfaceportion and the contact angle, the composite materials have highercontact angles if the proportion of the number of fluorine atoms at thesurface portion is 40% or more.

FIGS. 2 to 4 are microscopic photographs (magnification: 20 times). FIG.2 shows the contact state of a water droplet on the surface of anickel-polytetrafluoroethylene oligomer composite material having acontact angle of 173° according to the present invention. FIG. 3 showsthe contact state of a water droplet on the surface of the conventionalpolytetrafluoroethylene resin film having a number average molecularweight of more than 100,000 and a contact angle of 110°. FIG. 4 showsthe contact state of a water droplet on the surface of the conventionalnickel plating film having no fluorine compound dispersed therein and acontact angle of 67°.

We claim:
 1. A fluorine compound-containing composite material having acontact angle of 150° or more at the surface consisting essentially of ametal matrix and particles or fibers of a polytetrafluoroethyleneoligomer having a number average molecular weight of 10,000 or lessdispersed therein, the proportion of the number of fluorine atoms to thenumber of the total atoms at the surface portion of the compositematerial being 40% or more, wherein the surface portion is that portionof the composite material which extends from about 20 to about 40 Å intothe composite material from the surface of the composite material. 2.The composite material of claim 1, wherein the polytetrafluoroethyleneoligomer is in the form of particles having an average particle size of0.1 to 150 μm.
 3. The composite material of claim 2, wherein theproportion of the number of fluorine atoms to the number of total atomsis 40 to 60%.
 4. The composite material of claim 3, wherein theparticles have an average particle size of 0.1 to 15 μm.
 5. Thecomposite material of claim 4, wherein the contact angle is 160° ormore.
 6. The composite material of claim 3, wherein the particles havean average particle size of 0.1 to 4 μm.
 7. The composite material ofclaim 6, wherein the contact angle is 170° to 180°.
 8. The compositematerial of claim 1, wherein the number average molecular weight is1,000 to 10,000.
 9. The composite material of claim 1, wherein saidparticles or fibers of a polytetrafluoroethylene oligomer have beensurface treated with fluorine gas.
 10. A fluorine compound-containingcomposite material having a contact angle of 150° or more at the surfaceconsisting essentially of a metal matrix and particles or fibers of apolytetrafluoroethylene oligomer having a number average molecularweight of 10,000 or less dispersed therein, the proportion of the numberof fluorine atoms to the number of the total atoms at the surfaceportion of the composite material being 40% or more, said compositematerial being prepared by codepositing a metal film withpolytetrafluoroethylene oligomer particles or fibers having a numberaverage molecular weight of 10,000 or less to an article to be platedfrom a composite plating bath having said particles or fibers dispersedtherein, wherein the surface portion is that portion of the compositematerial which extends from about 20 to about 40 Å into the compositematerial from the surface of the composite material.
 11. The compositematerial of claim 10, wherein the polytetrafluoroethylene oligomer is inthe form of particles having an average particle size of 0.1 to 150 μm.12. The composite material of claim 11, wherein the proportion of thenumber of fluorine atoms to the number of total atoms is 40 to 60%. 13.The composite material of claim 12, wherein the particles have anaverage particle size of 0.1 to 15 μm.
 14. The composite material ofclaim 13, wherein the contact angle is 160° or more.
 15. The compositematerial of claim 11, wherein the particles have an average particlesize of 0.1 to 4 μm.
 16. The composite material of claim 15, wherein thecontact angle is 170° to 180°.
 17. The composite material of claim 10,wherein the number average molecular weight is 1,000 to 10,000.
 18. Thecomposite material of claim 10, wherein said particles or fibers of apolytetrafluoroethylene oligomer have been surface treated with fluorinegas.